Measuring sensors, particularly electrochemical measuring sensors, are widely used for quality monitoring, process control and research in agriculture, beverages, foods, water, various industries and research labs. Such measuring sensors include pH sensors. A critical component of a pH sensor is a pH glass membrane. Generally, pH glass material used in the pH glass membrane is specially formulated to make the material sensitive to hydrogen ions (H+).
Conventionally, to test and verify the proper functioning of a pH sensor, the sensor is placed in contact with a standard buffer solution of known pH (e.g., pH 4, 7 and 10 buffers), and the sensor's signal output is displayed and verified using a pH meter. Certain pH meters include a function to measure glass impedance. However, such meters are not accurate enough or capable to distinguish sensor failure modes, such as a crack in the glass membrane or a short circuit in the sensor.
If in case a sensor failed to work normally, for whatever reason (e.g., harsh application conditions, inappropriate selection of sensor type, manufacturing processes, changes of material/part supply etc.), physical examination and often destruction (e.g., dissection) of the sensor has previously been the only way to determine the failure mode and root cause of failure of the sensor. However, dissecting a pH sensor can be very time consuming. In addition, it is not guaranteed to see root cause after dissection. For example, a micro-crack at the pH glass membrane/glass stem interface in transversal direction may not be visible. More often, dissection can easily damage the signs of root cause because of the complex construction of a pH sensor, which is usually built with materials of wide range mechanical and physical properties—from liquid and soft rubber, to hard plastic, rigid epoxy, and very hard but brittle glass.
Accordingly, there remains a need for further contributions in this area of technology to enable a method to characterize failure modes and to determine the root cause of such failures a measuring sensor.